1. Field of the Invention
The present invention relates to a process for producing an ink jet recording head and more particularly to a process for producing orifices in the ink jet recording head.
2. Description of the Prior Art
Ink jet recording is a non-impact recording method which is almost free from noise generation during recording, which is capable of high-speed recording, and which enables recording without requiring any special operations for fixing onto ordinary paper. Of the currently known various recording methods, this method is very useful. Wide varieties of proposals have been put forward for this method and improvements have been applied to it. These efforts have led to some commercially available products, whereas some ideas are still on the way to commercialization.
Ink jet recording is one method in which ink droplets are ejected by various mechanisms and are deposited on a recording medium such as a paper, so as to perform recording.
A novel method relating to ink jet recording was proposed in Japanese Patent Application Laying-open No. 59936/1979, and its fundamental principle is outlined as follows: Thermal pulses as information signals are applied to the ink introduced in an ink passage that can accommodate the ink. As a result, the ink generates a vapor bubble and produces an actuating force during its growth and contraction. This force causes the ink to be ejected as the droplets from orifices communicating with the ink passage, whereafter the droplets are deposited on a recording medium to perform recording.
This method provides the orifices in a high-density, multi-array layout which can easily fit for high-speed recording as well as color recording. In addition, the apparatus employed in this method is simpler in construction than conventional apparatuses. Hence, a recording head can be reduced in size as a whole and is suitable for mass-production. This method can also easily provide a wide-range recording head in which many orifices are arranged by taking advantage of remarkable IC technologies and microscopic processing techniques and of an increase of reliabilities in the semiconductor field. Thus, the method is broad in the scope of applications.
As shown in FIG. 1, the ink jet recording head for use in ink jet recording is composed of a first substrate 101 (hereinafter to be referred to as a heater board) equipped with electro-thermal converting elements and a second substrate 102 which has grooves for forming a liquid chamber accommodating the ink and ink passages by joining the first substrate 101 to the second substrate 102. The second substrate 102 integrally has an orifice plate 104 which includes ink ejection outlets 109, that is, orifices, communicating with the ink passages (the second substrate will hereinafter to be referred to as a grooved top plate).
The heater board 101 is adhered and fixed to a supporting base plate 103 with the use of an adhesive. The grooved top plate 102 is bonded with the heater board 101 in such a manner that the electro-thermal converting elements disposed on the heater board 101 register with the grooves for ink passages formed in the grooved top plate 102. The orifice plate 104 of the grooved top plate 102 is disposed so as to project forward and downward like an apron from a front end surface of the supporting base plate 103.
Grooves 103A are formed in a part of the area of the supporting base plate 103 which is covered by the orifice plate 104, more specifically, in the area that is covered by right and left end portions of the orifice plate 104.
The ink is supplied from an ink feed member 105 through an ink feed port 102a provided in an upper portion of the grooved top plate 102. The ink feed member 105 has a projecting bar and is fixed to the supporting base plate 103 by inserting this projecting bar into a through hole provided in the supporting base plate 103 and thermally caulking the through hole.
The gaps 110a and 110b, between the ink feed member 105 and the heater board 101, and, between the ink feed member 105 and the grooved top plate 102, as well as a joining area with a tiny gap between the orifice plate 104 and the front end surface of the supporting base plate 103 which is to be sealed with an adhesive, constitute an adhesion space which is filled with a sealing compound from above the ink feed member 105 through the grooves 103A.
The ink jet recording head as described above has several problems with production as indicated below.
1) In FIG. 1, the joining area between the orifice plate 104 and the front end surface of the supporting base plate 103 has so small a gap that the sealing compound often fails to reach the gap, particularly, its central portion, in a sufficient amount. To avoid this problem, it has been a customary practice to lower the viscosity of the sealing compound. The lowering of its viscosity, however, causes the sealing compound to go out of holes provided in the supporting base plate 103, i.e. a mounting hole for a presser spring to be mounted to provide a close contact between the second substrate 102 with the ink passages and the heater board 101, and a hole for insertion of an ink supply pipe of the ink feed member 105 for suppling the ink from an ink tank, as well as a gap in a posterior portion of the ink feed member 105. As a result, the amount of the sealing compound may be insufficient. Moreover, a protrusion which will serve as a reference object when the ink jet recording head is mounted on the carriage may be coated with the sealing compound, thus deteriorating the accuracy and precision of mounting, thereby, for instance, causing a recorded line to be curved. Furthermore, the sealing compound may invade the orifices, causing the ink not to be ejected.
2) In bringing the electro-thermal converting elements and the orifices into registration, it has been a customary practice to register them manually using a specialized jig while alternately observing the electro-thermal converting elements and the orifices under a metallurgical microscope.
This manual adjustment by an operator for registration of the electro-thermal converting elements and the orifices has the following problems:
a) Variations in the manual work cause variations in the accuracy and precision of adjustment.
b) Visual measurements and manual operations of the jig for repeated use take much time for adjustment.
c) The operator suffers from asthenopia due to the long-term visual measurements, and ultraviolet irradiation for setting the adhesive when fixing the members after registration of the orifices and the electro-thermal converting elements.
To solve these problems, an apparatus has been proposed for performing registration of the orifices without relying on manual work. According to this apparatus, the positions of the electro-thermal converting elements and the positions of the orifices are confirmed with an ITV camera via an optical system, and information on the positions of them are converted into image signals, which are transmitted to an image processing unit. In the image processing unit, the image signals of the two members are processed and their positional coordinates are calculated. On the basis of the calculated results, the difference in position is determined, and the top plate is moved so that the positions of the electro-thermal converting elements and the positions of the orifices are brought into registration with each other.
This conventional apparatus still involves the following problems: Generally, the orifices formed in the orifice plate integral with the top plate and the grooves for the ink passages of the top plate are arranged in plural numbers with similar shapes. When these members are to be brought into registration in joining the top plate with the heater board while observing the orifices with the ITV camera, the determinations of the orifices to be registered have been impossible with a conventional image processing unit. Consequently, the electro-thermal converting elements and the orifices are generally out of register the orifice may be positioned at a place where the electro-thermal converting elements are not located, or no orifices may be positioned at a place where the electro-thermal converting elements are located. Such a failure in the accurate registration of the orifices and the electro-thermal converting elements will adversely affect ink ejection performance, and would become the cause of the ink not being ejected in the worst case. Particularly, when the ink jet recording head becomes more accurate, more precise and speedier, the orifices and the grooves for ink passages become micro-sized. This requires the exact registration between the orifices and the electro-thermal converting elements as an indispensable task for the production of the ink jet recording head.
3) When the orifices of the recording head are formed, it has been a common practice to use a laser capable of emitting an ultraviolet radiation such as a fourfold wave of an excimer laser or a YAG laser. The formation of the orifices in this case has been carried out in two roughly manners as follows.
a) First, the orifice plate for forming the orifices is joined to an end surface of the top plate where the groove for the ink passages has been formed. Then, the orifices are formed by irradiating a laser beam onto the orifice plate via a mask. The groove for the ink passages is open at the end surface of the top plate, and the formation of the orifices is performed so that the orifices will communicate with the opening. The orifice plate may be formed of a resin film or the like. During the formation of the orifices, the position of the orifice to be formed and the position of the groove for the ink passages are brought into registration.
The above-mentioned procedure is shown in FIG. 2. In this drawing, the reference numeral 301 denotes an ultraviolet laser apparatus, 302 a laser beam emitted by the ultraviolet laser apparatus 301, 303 a lens system, 304 a projection mask having aluminum evaporation-deposited thereon which has all or some of the patterns of the orifices and which can be shielded to the laser beam 302, 305 a top plate provided with a groove for the ink passages and a groove for a common liquid chamber, 305A an orifice plate, and 305B a support member for supporting the top plate 305. A movable stage 306 moves the support member 305B horizontally, thereby moving the top plate 305 supported thereon, and eventually adjusting the position of the groove for the ink passages with respect to the laser beams.
Details of the ink jet recording head body in which the orifices have been formed in accordance with such a construction are illustrated in FIG. 3.
FIG. 3 is a schematic sectional view of the recording head body.
In FIG. 3, 408 is a heater board with an electro-thermal converting element patterned, and 411 is an orifice formed in an orifice plate 405A. The reference numeral 414 designates an ink passage, and 415 is an electro-thermal converting element provided in correspondence to the ink passage 414. The ink passage 414 is composed of the groove for the ink passage and the heater board.
b) Alternatively, an orifice is formed by irradiating an ultraviolet laser beam from the side where the groove for the ink passage 414 has been formed, onto a member having the top plate 405 and the orifice plate 405A formed integrally. This procedure is illustrated in FIG. 4.
FIG. 4 shows a manner in which an ultraviolet laser beam is irradiated from the ink passage side onto the orifice plate formed integrally with the top plate, thereby forming an orifice. The same members as shown in FIG. 2 are indicated by the same reference numerals.
The procedure for forming the orifice as mentioned above has been performed in the following manner: A laser beam that has passed the projection mask is irradiated onto the orifice plate to form an orifice. For registration of the laser beam, the shape of the groove for the ink passage is incorporated as image informations by means of an ITV camera, and the position of the groove is confirmed by recognizing the image. Then, the position of the groove for the ink passage is brought into registration via the projection mask with the position where the laser beam is to be irradiated.
A third problem with the laser beam machining for forming orifices is as follows: Since there are a plurality of the grooves for the ink passages with the same shape, whichever the above-mentioned methods may be employed, it has been difficult to determine by image processing which of the grooves for ink passages should be registered with the laser beam.
For example, it has been conventionally used to form the orifices after counting the number of grooves for the ink passages from the end groove for the ink passage to the aimed groove for the ink passage, or to form the orifice after registering the top plate with a movable stage, and then irradiating the laser beam onto the orifice plate.
The former method, however, takes a wasteful time for the formation of the orifices because the number of grooves for the ink passages has to be counted from the end grooves for the ink passages to the aimed groove for the ink passage each time the orifice is to be formed.
On the other hand, according to the latter method, if the dimensions of the top plate are varied, the dimensions of the top plate mounting panel have to be varied with response to dimensional variation, or data on how much the movable stage should be moved must be incorporated again into the image recognition apparatus. Thus, the steps for laser beam machining become complicated.
4) Fourthly, there has been the problem that when orifices are to be formed by laser beam machining, their shapes may be different depending on the positions of the orifices arranged.
As shown in FIG. 5, a laser beam emitted by a laser oscillation apparatus (not shown) is divided into laser beams L.sub.1 to L.sub.n indicated by a plurality of thick arrows as shown in FIG. 5 that have passed the mask.
An optical axis 616.sub.k (indicated by a one dot chain line in FIG. 5) of the laser beam L.sub.k in the neighborhood of the center of the laser beam, coincides with an axis 620.sub.k of the orifice 611.sub.k, which is a symmetrical axis for the shape of the orifice, but the intensity of the laser beam becomes weaker at a peripheral portion apart from the center of the laser beam. Therefore, when the orifice plate 610 is formed, the shape of the orifice formed is such that its end heads toward the inside where the intensity of the laser beam is strong.
This trend is noticeable at orifices 611.sub.1 and 611.sub.n at both end portions. The axes of ink ejection outlets 620.sub.1 and 620.sub.n do not coincide with the optical axes 616.sub.1 and 616.sub.n of the laser beams L.sub.1 and L.sub.n and incline toward the center of the orifice. As a result, ink droplets are ejected more inwardly than the direction for ejecting ink droplets in the vicinity of the center of the laser beam. Furthermore, the orifices 611.sub.k-1, 611.sub.k, and 611.sub.k+1 in the neighborhood of the central axis of the laser beam, and the orifices 611.sub.1, 611.sub.n at peripheral portions of the laser beam are different in the direction of laser beam machining and have different shapes. This also results in the deterioration of the grade of recorded images.
To solve the above-described problems, the following methods have been adopted:
The orifice plate is machined only with use of laser beam in the neighborhood of the center of the laser beam to form an orifice. The orifice plate is laser beam machined in such an manner that an optical system thought out so that the intensity of the laser beam at peripheral portions of the laser beam coincides with the intensity in the neighborhood of the center of the laser beam, thereby to form an orifice. According to the method for forming the orifice using only the laser beam in the neighborhood of the center of the laser beam, however, the area where the orifice is formed is narrow, thus making it impossible to form a number of orifices at a time. The formation of multiple orifices requires that the area of laser beam machining be varied frequently, and the orifice plate be machined for many times. Consequently, the machining time is prolonged, and the throughput is decreased. At each laser beam machining, moreover, there tends to be large variations in the positions, shapes and diameters of the orifices, thus lowering the accuracy and precision of machining.
The method of working out such an optical system that the intensity of the laser beam is the same in the vicinity of the center of the laser beam and at the peripheral portions of the laser beam has the following disadvantages: Since the construction of the optical system is complicated, many lenses are used, thus making their adjustment difficult and decreasing the throughput. Also, the apparatus is separately needed to adjust the optical system, thereby rising the costs of the orifice formation.
5) Laser beam machining for orifice formation also has the following problems:
When a workpiece such as an ink jet recording head is to be laser beam machined to form orifices, the formation of numerous orifices takes much time such a construction in which a laser beam is converged to one point to form orifices one by one. Particularly, much time is required for registration intended for accurate laser beam machining of an orifice, thus lowering remarkably the operational efficiency. To avoid these disadvantages, a laser beam machining apparatus is conceivable in which a desired number of orifices can be perforated in the work, or in which the position of the orifice is measured, and its position can be corrected on the basis of the results measured. In such an apparatus, the orifices with the intended diameter or area are perforated under the conditions where the laser power and/or the irradiation time with response to the thickness of the orifice plate are setted in advance.
In the laser beam machining apparatus as mentioned above, however, it may be difficult to perforate orifices with the same diameter or area under the same conditions for long periods of time, owing to variations in the thickness of the orifice plate according to lot differences, changes in the laser power due to changes with time in the laser oscillator and so forth. Hence, regular sampling may become necessary to reset the laser power and/or the irradiation time. This resetting step may lower the operating efficiency of the apparatus. In addition, whenever the lot of the top plate is changed and the interval of the grooves is changed, resetting must be done manually. When many top plates are to be formed from one lot, in particular, an operational step for setting the laser power for each top plate will become necessary. Such preparatory tasks for the apparatus are laborious, thereby lowering the operating efficiency.